1. Field of the Invention
The present invention relates generally to protecting downhole components from shock and vibration while drilling a well and, in particular, to a method and apparatus for protecting measurement while drilling equipment from shock and vibration using a locking mule shoe system.
2. Description of the Prior Art
In the drilling of deep bore holes for the exploration and extraction of crude oil and natural gas, the “rotary” drilling technique has become a commonly accepted practice. This technique involves using a drill string, which consists of numerous sections of hollow pipe connected together with a drill bit being located at the bottom end. The rotation and compression of the drilling bit causes the formation being drilled to be successively crushed and pulverized. Drilling fluid, frequently referred to as “mud”, is pumped down the hollow center of the drill string, through nozzles on the drilling bit and then back to the surface around the annulus of the drill string. This fluid circulation is used to transport the cuttings from the bottom of the bore hole to the surface where they are filtered out and the drilling fluid is re-circulated as desired. The flow of the drilling fluid, in addition to removing cuttings, provides other secondary functions such as cooling and lubricating the drilling bit cutting surfaces and exerts a hydrostatic pressure against the bore hole walls to help contain any entrapped gases that are encountered during the drilling process.
Since the advent of drilling bore holes, the need to measure certain parameters at the bottom of the bore hole and provide this information to the driller has been recognized. These parameters include, for example, the temperature and pressure at the bottom of a bore well, the inclination or angle of the bore well, the direction or azimuth of the bore well, and various geophysical parameters that are of interest and value during the drilling process. The challenge of measuring these parameters in the hostile environment at the bottom of the bore well during the drilling process and somehow conveying this information to the surface in a timely fashion has led to the development of many devices and practices over the years.
The general class of tools used today to send data from the bottom of the well to the surface while drilling are referred to as “measurement while drilling” (hereafter “MWD” tools). Types of MWD tools contemplated by the prior art have been such things as electromagnetic waves or EM (low frequency radio waves or signals, currents in the earth or magnetic fields), acoustic (akin to sonar through the mud or pipe and using mechanical vibrations) and pressure or mud pulse (sending pulses through the mud stream using a valve mechanism).
Downhole tools of the above type are subjected to substantial forces and vibration during drilling. Sensor packages and other sensitive downhole electronics, such as those housed in measurement-while-drilling (MWD) tools, steering tools, gyros, or logging-while-drilling (LWD) tools, are particularly vulnerable to damage from vibration and shock during drilling. Unless the electronics in downhole tools are mounted in such a way as to reduce the vibration and shock that is felt by the electronics, the vibration and shock will ultimately reduce the life cycle of the electronics, as well as adding fatigue and wear to the bottom hole assembly. Reducing shock and vibration felt by the electronics extends their life cycle, which saves valuable time and money that would be spent replacing or repairing the directional sensors and electronics. Accordingly, additional measures to minimize shock and vibration that reaches electronics are needed.
One common feature of MWD tools of the type under consideration is to provide a mechanism for orienting the tool downhole. In order to ascertain the angular orientation of a drill bit, or the like, it is common practice in the art to dispose a radially inwardly extending camming member within a bore extending through the tool string. The camming member may be a key, a spline surface, or the like. The camming member is usually in a predetermined angular orientation with respect to the drill bit or member whose orientation it is desired to ascertain. For example, the “lower end assembly” of such tools often terminate at the bottom end in a “mule shoe” arrangement. The mule shoe internal bore receives what is called a pulser helix which is, in turn, attached to a poppet housing. The pulser helix has an axially extending camming surface which contacts the camming member inside the mule shoe as the pulser helix is inserted within the bore of the mule shoe. Abutting engagement of the camming surface and camming member acts to rotate the directional drilling assembly. When the camming surface and camming member are fully engaged, the directional ascertaining element of the assembly may accurately plot or record the orientation at which the camming member, and therefore the drill bit, are disposed relative to a predetermined datum.
Even though the pulser helix may be affixed to the mule shoe with a key arrangement or the like, some movement and vibration are still possible. For example, some oil and gas exploration and production companies at the present time use vibrating devices known as “agitators” to increase penetration rates while drilling wells. Agitators typically operate or reciprocate between about 12 and 26 hertz during drilling operations, and constantly vibrate at these frequencies. Accordingly, agitators provide additional shock and vibration throughout the drill string that improve drilling performance. However, these devices can cause damage to or the failure of the sensitive downhole components used in the MWD systems. Such sensitive electronic components of the MWD systems may be subjected to g-force vibration and shock on the order of 100 g's in amplitude.
Thus, despite improvements that have been made in MWD systems, a need continues to exist for a method and improved apparatus for further reducing shock and vibration in such devices in use.